In a motor vehicle electrical system, over-voltage protection circuitry is needed to protect electrical loads from damage due to over-voltages that can occur during jump-starting and load-dump conditions. Also, the protection circuitry must be active at all times since certain electrical loads (an engine control module, for example) are designed to be powered even during periods of vehicle inactivity. Although passive shunt suppression devices such as Zener diodes or MOVs can be used in certain applications, the transient over-voltage energy can be too high to clamp with shunt devices, particularly in heavy duty vehicle applications. In such applications, a series-pass suppression device such as a linear transistor may be more suitable than a shunt device. However, series-pass suppression circuits typically draw relatively high quiescent current and exhibit slow response to transient voltages. The high quiescent current draw makes the typical series-pass suppression circuit impractical for powering loads during periods of vehicle inactivity, and the slow response to transient voltages can result in transient over-voltage “shoot-through” prior to controlled suppression. Accordingly, what is needed is a series-pass over-voltage suppression circuit that has low quiescent current draw, and that exhibits a fast response to transient over-voltages for minimizing transient over-voltage shoot-through.